Basically the flash unit mecablitz 52 AF-1 digital for Pentax also can be used together with the digital-camera Pentax K-1. However, this flash unit is equipped with an autofocus-measuring beam comparable to the Pentax flash units AF540FGZ and AF360FGZ. Unfortunately the Pentax K-1 isn’t equipped with the control of such autofocus-measuring beam of an external flash unit. Therefore the AF-measuring beam of the flash unit mecablitz 52 AF-1 digital and also of the Pentax flash units AF540FGZ respectively AF360FGZ isn’t controlled by this camera. Normally the Pentax K-1 works with the built-in AF-measuring beam in that case. This also can’t be changed by the firmware of the external flash unit.

I'll have to see if there's a way to set the camera so the green beam shoots when a flash is mounted.